Musannaf Ibn Abi Shayba 26:135

Jarir narrated to us, from Mansur, from Ibrahim, from Alqama, who said: Ibn Mas’ud was approached regarding a mother and maternal half-siblings. He gave the maternal half-siblings one-third, and he gave the mother the remainder of the wealth. And he said: "The mother is the *‘asaba* (residuary heir) for the one who has no *‘asaba*."